It is well known that placing an elongated obstruction transverse to the direction of fluid flow within a conduit will result in the generation of vortices in the wake of the obstruction. The vortices are induced by and shed alternately from opposite sides of the obstruction, which is called a bluff body or vortex generating element. This has been referred to as the Karman effect. The frequency of the vortex shedding is proportional to the width of the bluff body and the velocity of flow, so that detecting the frequency of the detected vortices can generate signals indicative of fluid flow velocity.
Various flow meters have been developed to measure flow based on the recognized Karman effect. Despite the multitude of differently constructed flowmeters, there is still a further need to provide an improved flowmeter, and especially an improved flow meter which is of the insertion-type, i.e., a universal flow meter directly insertable into pipes or conduits with different diameters rather than being constructed in a casing having a pre-determined diameter to match the pipe next to which it is applied, i.e., the casing carrying the flow meter must be adapted to fit more or less flush between two joining pipe sections. Such insertion-type flow meters are advantageous since they eliminate the need to change the dimensions and construction of the flow meter and casing according to the diameter of the pipe to which they are applied. Thus, insertion-type flow meters are generally more cost effective since it is not necessary to purchase a different size flow meter for a given diameter. Moreover, such an insertion type flow meter is easily insertable and removable from a pipe for easy access for repairs, replacement or the like.
However, a major shortcoming of flowmeters designed to detect vortex shedding arises from external forces and accelerations in the attached piping systems. Because the physical detection member of a vortex flowmeter is designed to be deflected by the vortices, any other forces which would cause deflection, such as external vibration of the conduit, non-uniform flow, etc. may be detected as well. This is especially true at lower fluid velocities when the vortex strength is diminished and the effect of the external forces has a greater effect. The external forces (the “noise”) thereby adversely affect the accuracy of the signal generated by the physical member. Although many compensating methods have been employed to minimize the noise effect, each has the potential for only small or inadequate reduction of the influences of noise.
Not only is there a need to provide an improved insertion-type flow meter with the aforementioned advantages, but there has also been a need to eliminate the problems associated with vortex shedding flow meters heretofore which do not adequately compensate for flow disturbances which interfere with the measurement of the vortices and thereby producing inaccurate measurements of fluid velocity. In this regard, it is desirable to provide a flow meter configured for minimizing or compensating for unwanted fluid pulsations and vibrations that can occur within the conduit as well as other forms of fluid noise which tend to interfere with the accuracy and operation of the flow meter.
What is needed is an insertion vortex meter configured for generating a vortex signal that reduces the effect of noise while still generating a uniform signal for a wide range of velocities of fluid flow.